#include <iostream>
#include <stdio.h>

using namespace std;

int main() {
    int a = 1,b = 1,c = 1,n;
    cin >> n;
    for(int i = 2 ; i < n ; i ++){
        c  = a + b;
        a = b;
        b = c;
    }
    cout << c;
    return 0;
}